Abstract: The invention relates to a process for identifying microorganisms by means of mass spectrometry, especially by means of MALDI-TOF-US. According to the invention, a data base (DB) is used that comprises synthetic reference spectra (REFs) of known microorganisms, which are formed by combination of a number, reduced relative to natural mass spectra (REFN), of signals (S) that are specific to the respective microorganism, as well as difference spectra (DIF), which are formed by offsetting in each case two synthetic reference spectra (REFS) of the known microorganisms. The process also comprises a first analysis step, in which a similarity analysis of a sample mass spectrum (SAM) of a microorganism that is to be identified is performed with synthetic reference spectra (REFS) that are contained in data base (DB), and a second analysis step, in which a similarity analysis of sample spectrum (SAM) is performed with at least a portion of difference spectra (DIF) that are contained in data base (DB).